The present invention relates to an electron microscope for performing CD measurement of semiconductor patterns having various kinds of shapes and dimensions, and more particularly to a scanning electron microscope having a function suitable for managing the measurement precision, and to a method for evaluating accuracy of repeated measurement using the scanning electron microscope.
In a semiconductor wafer manufacturing process, the microminiaturization of thin film patterns which are formed on a wafer in a multilayer structure rapidly progresses. Accordingly, the importance of process monitoring which monitors whether or not those patterns are formed on the wafer according to the design is more and more increasing. Above all, as far as transistor gate wiring and metal wiring made of aluminum, copper, or the like formed on a wafer, are concerned, there is a close relationship between the line width and device operation characteristics, and therefore manufacturing process monitoring of the line width is in particular important.
As a measurement tool for measuring the line width of the micro-minute wiring on the order of tens of nanometers, the scanning electron microscope (measurement SEM (Scanning Electron Microscope)), or the CD (Critical Dimension) SEM, which is used for measuring the line width and is capable of imaging the wiring with the magnification of from 100000 to 200000 times, is conventionally used. An example of measurement processing which uses such a scanning electron microscope is described in Japanese Patent Laid-Open No. Hei 11-316115. In the disclosed example of this document, from a local area in an image acquired by imaging a wiring line to be measured, image signal profiles of the wiring line are added and are averaged in the longitudinal direction of the wiring line to create a projection profile, and a wiring dimension is then calculated as a distance between right and left wiring edges detected in this profile. In addition, in the disclosed example of Japanese Patent Laid-Open No. Hei 11-316115, there is provided a function of displaying, on the same screen, the formed image, and the local area where the projection processing has been performed. Thereby, a user can check now easily about which wiring part was measured in the screen.
Incidentally, important indicators for evaluating measurement performance of CDSEMs include measurement repeatability. This measurement repeatability is expressed as the variation in measurements when measuring the same wiring a plurality of times. A smaller value of the variation means that the measurement performance is higher. Because semiconductor patterns to be measured are more and more microminiaturized, the measurement repeatability is more severely required for the CDSEMs.
Thus, it is considered that in future the requirements for the repeatability are severer and the amount of roughness tends to increase because a resist material which is sensitive to exposed illumination is used to create micro-minute patterns. Accordingly, it is expected that in future a measurement error caused by the influence of fluctuations in micro-minute shape cannot be ignored in association with a dimension error which a CDSEM might generate.